Rear wheel suspension for a motorcycle

ABSTRACT

An improved rear wheel suspension for a motorcycle is provided which includes a body frame, a rear wheel support frame such as a rear fork pivotally mounted on the body frame for upward and downward movement relative thereto and rotatably supporting a rear wheel, at least one rear shock absorber disposed between the body frame and the rear wheel support frame for damping the relative movement between the body frame and the rear wheel, and a mechanism for adjusting the damping force of the rear shock absorber in a manner such that the rate of increase in the compression stroke of the rear shock absorber is increased in proportion to the upward movement of the rear wheel relative to the body frame.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a rear wheel suspension for a motorcycleadapted to effectively absorb shock imposed on a rear wheel for improvedriding comfort even with variation in load on the motorcycle.

2. Description of the Prior Art

In the past, there has been known a rear wheel suspension for amotorcycle in which a rear wheel support frame such as a rear forksupporting a rear wheel is mounted on the body frame at the rear portionthereof for up and down swinging movement and in which a rear shockabsorber is connected between the body frame and the rear wheel supportframe. However, such a prior art rear wheel suspension isdisadvantageous in that the greater the load on the motorcycle, theworse becomes the riding comfort.

SUMMARY OF THE INVENTION

The present invention is intended to obviate the above disadvantage andhas for its object the provision of an improved rear wheel suspension ofthe kind described which is capable of improving the riding comfort andrunning performance of the motorcycle by increasing the rate of increasein compression stroke of the rear wheel shock absorber in proportion tothe increasing upward displacement of the rear wheel relative to thebody frame to thereby enable the rear shock absorber to absorb thegreater amount of shock in an effective manner.

Another object of the invention is to provide a rear wheel suspension ofthe kind described in which the rate of increase in compression strokeof the rear shock absorber can be readily adjusted to a desired value.

A further object of the invention is to provide a rear wheel suspensionof the kind described which is small in size and adapted forinstallation in a limited available space, light in weight, excellent indurability and can perform the intended function for long periods ofuse.

The above and other objects, features and advantages of the inventionwill become apparent from the following detailed description of theinvention when taken in conjunction with the accompanying drawings whichillustrate several presently preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate a preferred embodiment of the presentinvention;

FIG. 1 is a side view of a motorcycle equipped with a rear wheelsuspension constructed according to the invention;

FIG. 2 is an enlarged view of the essential parts of the suspension ofFIG. 1, showing its operating state;

FIGS. 3 and 4 illustrate another embodiment of the invention;

FIG. 3 is a side view of a motorcycle equipped with a modified form ofrear wheel suspension according to the invention;

FIG. 4 is a partial view of the suspension as taken from the line IV--IVof FIG. 3;

FIG. 5 is a graphic representation showing the relationship between thedisplacement of a rear wheel and the compression stroke of the rearshock absorber;

FIGS. 6 and 7 illustrate a further embodiment of the invention;

FIG. 6 is a side view of a motorcycle equipped with another form of rearwheel suspension according to the invention;

FIG. 7 is an enlarged view of the essential parts of the suspension ofFIG. 6, showing its operating state; and

FIG. 8 illustrates a further modified form of rear wheel suspensionaccording to the invention, showing the same operating state as FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, same reference numerals are given to the similar orcorresponding elements throughout the several embodiments of theinvention.

A first embodiment of the invention will now be described with referenceto FIGS. 1 and 2.

Reference numeral 1 indicates a body frame of a motorcycle, to the rearportion of which is pivotally connected at 2 a rear wheel support frameor a rear fork 3 at the forward end thereof for relative upward anddownward swinging motion. The rear fork 3 has a pair of side forksections between which a rear wheel 4 is rotatably supported.

Rotatably mounted at 6 on the respective side fork sections of the rearfork 3 are a pair of lever plates 5 each in the form of a invertedtriangle at their intermediate corners, each of which lever plates has afirst or rear arm pivoted at 9 to a rear shock absorber 7 and a secondor forward arm pivoted to a pull rod 10 at a pivot point 11 lying abovethe pivot connection 9. The shock absorbers 7 extend forwardly andupwardly from the lever plates 5 and pivotally connected at 8 to theopposite sides of the rear upper portion of the body frame 1. The pullrods 10 extend forwardly and downwardly from the pivot connection 11 andare pivotally connected at 12 to the rear lower portion of the frame 1.

Turnably mounted on the body frame 1 at its forward end is a front fork13 which rotatably supports a front wheel 14.

FIG. 2 shows the operating relationship between the rear fork 3, therear shock absorbers 7, the lever plates 5, and the pull rods 10, takenwhen the rear wheel 4 swings up and down with respect to the bodyframe 1. When the rear wheel 4 is caused to move up and down relative tothe body frame 1 during travel of the motorcycle, the rear fork 3 isswung upwardly and downwardly around the pivot point 2 so that the shockabsorbers 7 contract and expand to absorb impactive loads to betransmitted to the body frame 1, as detailed later with reference toFIG. 2.

As the rear fork 3 is swung upwardly from the solid line position (lowerposition) to the chain-dotted line position (upper position), theinverted triangular-shaped lever plates 5, pivoted to the intermediateportions of the opposite side sections of the rear fork 3, are movedupwardly along with the rear fork 3 so that the forward arms of thelever plates 5, pivoted at 11 to the pull rods 10, are gradually pulledforward in accordance with the upward movement of the lever plates 5 torotate the latter around the pivot points 6 in the counterclockwisedirection. As a result, the amount of contraction of the rear shockabsorbers 7, pivoted at 9 to the rear arms of the lever plates 5, isequal to the sum of the amount of movement of the pivot connection 9 dueto the upward movement of the rear fork 3, and the amount of rotation ofthe pivot connection 9 due to the counterclockwise rotation of the leverplates 5. As the rate of displacement of each of the pivot connections 9in the direction of the axis of each shock absorber 7 due to therotation of the lever plates 5 increases in proportion to the upwardmovement of the rear fork 3, the rate of increase in contraction of theshock absorbers 7 is increased in accordance with the upward movement ofthe rear wheel 4. This is graphically illustrated in FIG. 5 in whichreference characters L and δ represent the upward displacement of therear wheel 4 and the amount of contraction of the shock absorbers 7,respectively. As apparent from this Figure, the contractioncharacteristic of the rear shock absorbers 7 is shown by a paraboliccurve. This means that as the amount of the upward movement of the rearwheel 4 is made greater due to the increase in loads imposed on the bodyframe 1 and/or due to the increase of external forces acting from theroad surface on the rear wheel 4, the amount of contraction of the rearshock absorbers 7 is accordingly increased to render their dampingcharacteristic harder so that the greater quantity of impactive forcesexerted on the rear wheel 4 can be absorbed effectively to therebyimprove the riding comfort and running performance to a substantialextent irrespective of variations in load on the body frame 1. In thiscase, during contracting movement of the rear shock absorbers 7, thepull rods 10 are subjected only to tensile forces but not to twisting orbending forces and therefore can be constructed to have a relativelysmall cross section with a strength enough to withstand the tensileforces acting thereon.

FIGS. 3 and 4 represent a second embodiment of the invention, in which arear wheel support frame such as a rear fork 3 includes a pair of sidefork members each in the form of a triangle. A bellcrank-shaped lever 5is rotatably mounted at 6 on the triangular side fork members of therear fork 3 at their top corners and has a forward arm pivoted at 11 toa pull rod 10, which is pivotally connected at 12 to the body frame 1,and a rear arm pivoted at 9 to the rear end of a single shock absorber 7which is arranged on a vertical plane passing through the centrallongitudinal axis of the body frame 1 and which is pivotally connectedat 8 to the rear upper portion of the body frame 1. The operation ofthis embodiment is the same as that of the aforementioned firstembodiment. Namely, as the rear fork 3 swings upwardly around the pivotconnection 2, the lever 5 is caused to rotate in a counterclockwisedirection relative to the rear fork 3 under the action of the pull rod10 whereby the amount of movement of the pivot connection 9 is equal tothe sum of the upward displacement of the rear fork 3 and the amount ofrotation of the lever 5.

FIGS. 6 and 7 show a third embodiment of the invention. In thisembodiment, a rear fork 3 supporting a rear wheel 4 is rotatably mountedat its forward end on the rear lower portion of the body frame 1 bymeans of a pivot connection 2 and has a forward extension 3' formedintegrally therewith and projecting forwardly from the forward endthereof.

A pair of shock absorbers 7 are pivotally connected at their lower endwith the opposite side sections of the rear fork 3 at the intermediateportions thereof and extend forwardly and upwardly therefrom so as to bepivotally connected at their upper ends with a lever plate 110 at itsmiddle, which is pivotally mounted at 8 on the rear upper portion of thebody frame 1 and extends forwardly and downwardly therefrom so as to bepivotally connected at 113 with a pull rod 112 which in turn is pivotedat 114 to the extension 3' of the rear fork 3.

FIG. 7 illustrates the operating relationship between the rear fork 3,the shock absorbers 7, the lever plate 110 and the pull rod 112, astaken when the rear wheel 4 swings up and down relative to the bodyframe 1. When the rear wheel 4 is caused to move upwardly and downwardlyrelative to the body frame 1 during travel of the motorcycle, the rearfork 3 is swung up and down around the pivot point 2 to absorb impactiveforces transmitted to the body frame 1 by expansion and contraction ofthe rear shock absorbers 7 in the manner as described below in detail.

When the rear fork 3 swings upwardly from the solid line position (lowerposition) to the chain-dotted line position (upper position), as shownin FIG. 7, the rear shock absorbers 7, pivotally connected to theopposite side sections of the rear fork 3, are compressed and at thesame time the extension 3' of the rear fork 3 is rotatedcounterclockwise about the pivot point 2 to a lower position so that thepull rod 112, pivoted at 114 to the extension 3' of the rear fork 3, ispulled downwardly to swing the lever plate 110 downwardly in acounterclockwise direction about the pivot connection 8 to furthercompress the shock absorbers 7. As a result, the amount of compressionor contraction of the rear shock absorbers 7 becomes equal to the sum ofthe amount of displacement of the pivot connection 108 due to the upwardswing of the rear fork 3 and the amount of displacement of the pivotconnection 109 due to the downward swing of the lever plate 110, wherebythe amount of contraction of the rear shock absorbers 7 is increased inpropotion to the upward movement of the rear wheel 4 while at the sametime the rate of increase in contraction of the shock absorbers 7 isincreased in accordance with the increasing upward displacement of therear fork 3. In this case, the relationship between the amount ofcontraction of the shock absorbers 7 and the upward displacement L ofthe rear wheel 4 is the same as shown in FIG. 5. Thus, the contractioncharacteristic of the rear shock absorbers 7 according to thisembodiment exhibits a parabolic curve.

In this connection, it is to be noted that the shock absorbers 7 may bepivotally connected at 113 instead of 109 to the lever plate 110, thepull rod 112 being pivoted at 109 instead of 113 to the lever plate 110.This arrangement operates substantially in the same manner as does thearrangement shown in FIGS. 6 and 7.

FIG. 8 illustrates a modification of the third embodiment as shown inFIGS. 6 and 7. In this modification, a lever plate 110 is pivotallymounted at 8 on the rear upper portion of the body frame 1 and extendsrearwardly therefrom for pivotal connection at 109' with the upper endsof a pair of rear shock absorbers 7 which are in turn pivotallyconnected at 108 to the opposite side sections of a rear fork 3. A pullrod 112 pivoted at 114 to an extension 3' of the rear fork 3 ispivotally connected at 113' to the middle portion of the lever plate110. The operation of this modification is the same as that of theaforementioned third embodiment as shown in FIGS. 6 and 7. Namely, asshown in FIG. 8 in the chain-dotted line, when the rear fork 3 is swungupwardly around the pivot connection 2, the lever plate 110 is pulleddownwardly to rotate in a clockwise direction around the pivot point 8by the action of the pull rod 112 whereby the rear shock absorbers 7 arecompressed by means of both the downward movement of the lever plate 110and the upward swing of the rear fork 3.

It is possible to arrange the shock absorbers 7 and the pull rod 112 ina manner such that the shock absorbers 7 are pivotally connected at 113'instead of 109' to the lever plate 110 and the pull rod 112 is pivotedat 109' instead of 113' to the lever plate 110 with substantially thesame operation as in the arrangement of FIG. 8.

In the embodiments as illustrated in FIGS. 6 to 8, a pair of shockabsorbers are employed but a single shock absorber may be usedsatisfactorily as in the case of the FIG. 3 embodiment.

In the foregoing description, though the rear fork 3 is used as the rearwheel support frame, a swing arm of cantilever type may be used in placethereof which acts to support the rear wheel only at one side of thebody frame.

To summarize, according to the present invention, lever plate means isarranged such that it is rotated relative to a rear wheel support framein accordance with the upward swing of the latter to impart acompressive force to rear shock absorber means disposed between the bodyframe and the rear wheel support frame, as a consequence of which itbecomes possible to set the rate of increase in the compression strokeof the shock absorber means at any desired value in a simple and easyway, thus improving the riding comfort and running performance of themotorcycle irrespective of the variation of loads carried thereon.

Further, since pull rod means, serving to impart torque to the leverplate, is subjected only to a tensile force but not to twisting, bendingor like other undersirable forces and hence can be formed of arelatively small rod having a limited cross sectional area, which, incombination with the lever plate means formed in a reduced size, makesit possible to fabricate the entire device in a very compact andlight-weighted manner adapted for installation thereof in a limitedspace without increasing the total weight of the motorcycle.

Moreover, the triangular-shaped construction of the lever plate meansserves to inhance the strength thereof, improving, in cooperation withthe fact that the pull rod means is acted upon only by a tensile force,the durability of the device as a whole.

While several presently preferred embodiments of the invention have beenshown and described, it will be evident to those skilled in the art thatvarious changes or modifications may be made therein without departingfrom the spirit or scope of the invention as defined in the appendedclaims.

What is claimed is:
 1. A rear wheel suspension for a motorcyclecomprising a body frame, a rear wheel support frame pivotally mounted onsaid body frame for upward and downward movement relative thereto androtatably supporting a rear wheel, rear shock absorber means disposedbetween said body frame and said rear wheel support frame for dampingthe relative movement between said body frame and said rear wheel, meansfor adjusting the damping force of said shock absorber means in a mannersuch that the rate of increase in the compression stroke of the shockabsorber means is increased in proportion to the upward movement of saidrear wheel relative to said body frame, said means for adjusting thedamping force of said shock absorber means comprises lever plate meanspivotally mounted on a rear upper portion of said body frame, anextension formed integral with said rear wheel support frame andprojecting forwardly therefrom beyond the pivot connection thereof withthe body frame, pull rod means pivoted at its one end to said leverplate means and at its other end to said extension, said rear shockabsorber means being pivotally connected at its one end to said leverplate means and at its other end to said rear wheel support frame at itsintermediate portion.
 2. A rear wheel suspension for a motorcycle as setforth in claim 1, wherein said lever plate means is pivotally mounted atits rear end on the rear upper portion of said body frame and extendsforwardly therefrom for pivot connection at its forward end to said pullrod means, and said shock absorber means is pivotally connected to anintermediate portion of said lever plate means lying between saidforward and rear ends.
 3. A rear wheel suspension for a motorcycle asset forth in claim 1, wherein said lever plate means is pivotallymounted at its forward end on the rear upper portion of said body frameand extends rearwardly therefrom for pivot connection at its rear end tosaid rear shock absorber means, and said pull rod means is pivoted to anintermediate portion of said lever plate means lying between saidforward and rear ends.